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Quenched microemulsions: a new route to proton conductors Cecile Noirjean,a Fabienne Testard,a Jacques Jestin,b Olivier Tache´,a Christophe Dejugnatc and David Carriere*a Solid-state proton conductors operating under mild temperature conditions (T < 150 C) would promote the use of electrochemical devices as fuel cells. Alternatives to the water-sensitive membranes made of perfluorinated sulfonated polymers require the use of protogenic moieties bearing phosphates/ phosphonates or imidazole groups. Here, we formulate microemulsions using water, a cationic surfactant (cetyltrimethyl ammonium bromide, CTAB) and a fatty acid (myristic acid, MA). The fatty acid acts both as an oil phase above its melting point (52 C) and as a protogenic moiety. We demonstrate that the mixed MA–CTA film presents significant proton conductivity. Furthermore, bicontinuous microemulsions are found in the water–CTAB–MA phase diagram above 52 C, where molten MA plays both the role of the oil phase and the co-surfactant. This indicates that the hydrogen-bond rich MA–
Received 18th April 2014 Accepted 4th June 2014
CTA film can be formulated in the molten phase. The microemulsion converts into a lamellar phase upon solidification at room temperature. Our results demonstrate the potential of such self-assembled
DOI: 10.1039/c4sm00849a
materials for the design of bulk proton conductors, but also highlight the necessity to control the
www.rsc.org/softmatter
evolution of the nanostructure upon solidification of the oil phase.
Introduction Fuel cells, which convert chemical energy from fuel (e.g., hydrogen or methanol) into electric energy, exhibit performances directly linked to the specic properties of the separator between the anode and the cathode. In PEMFCs (Proton Exchange Membrane Fuel Cells), the separating membrane must show bulk proton conductivity as high as possible, in addition to a lack of electronic conductivity and low permeability to gases and/or liquids.1 The most famous benchmark membrane operating at low temperatures (10 nm). This demonstrates that phase separation between the lamellar phases occurs, similar to the emulsication failure in the classical all-liquid microemulsions stabilized e.g. by n-alkyl poly(ethoxy) surfactants.17,22 In an opposite manner, the second phase transition is assigned to the melting of the mixed amphiphilic lm, but occurs without detectable structural changes (i.e. no curvature change): neither the microemulsion periodicity nor its correlation length as determined are affected (Fig. 3a and b, and Table 1) despite the well-dened endothermic peak (Fig. 5). This lack of response originates from the nature of the high-temperature transition occurring in the lm at 70 C, which we have elucidated using IR spectroscopy as a function of temperature.
Elucidation of the higher temperature transition At low temperature (T < 52 C), the mixtures therefore consist of a solid mixture of myristic acid and the MA–CTA–H2O lamellar phase. These lamellar structures vanish simultaneously and form the microemulsion at a melting temperature that coincides with that of myristic acid (Tm ¼ 52 C). This suggests that myristic acid alone melts at the rst transition and that the mixed lamellar phase organizes at the water/liquid MA interface. The second thermodynamic transition (Tm ¼ 70 C) is not accompanied by any detectable change in the nanostructure. This suggests that it corresponds to a transition of the MA–CTA interfacial lm. This interpretation is supported by infrared spectroscopy results as a function of temperature (Fig. 6). In the 1600–1800 cm1 range, characteristic of the carbonyl C]O vibrations (stretching), three series of spectra are observed. They are respectively characteristic of the mixtures below and above both thermal transitions. Below 52 C, the spectra are dominated by the vibrations at 1689 cm1 and 1701 cm1, assigned to MA cyclic dimers in the solid phase,23 and a band at 1724 cm1. The latter wavenumber value is an intermediate between that of the strongly bound cyclic MA dimers, and that of the free monomers24 (1774 cm1 and 1785 cm1). The band at 1724 cm1 is therefore assigned to the C]O vibrations in the mixed CTA–MA lamellar phase. Above the low-temperature phase transition (52 C), the vibrations assigned to the myristic acid cyclic dimers (1689 cm1 and 1701 cm1) strongly decrease (Fig. 6b, squares), whereas the vibration assigned to the MA–CTA complex
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acids.25 Furthermore, the formation or destruction of such a hydrogen bond network is expected to alter only marginally the bending modulus of a mixed equimolar MA–CTA bilayer.26 Assuming similar behaviour for monolayers, we elucidate the absence of nanostructure modication as the higher-temperature transition is crossed (Fig. 3 and 4).
Fig. 6 Infrared spectra of a MA–CTAB–H2O ¼ 70/19/11 weight% mixture as a function of temperature. (a) IR spectra in the carbonyl C]O stretching vibration region at different temperatures (full lines: in the 25–55 C range; dashed lines: in the 55–65 C range; dotted lines: in the 70–80 C range). (b) Relative area of the peaks as a function of temperature (squares: myristic acid dimers, 1701 and 1689 cm1; circles: 1724 cm1; triangles: 1709 cm1).
increases (1724 cm1, Fig. 6b, circles). This is consistent with the melting of the solid MA, and with an increased fraction of MA in interaction with CTAB by uptake of MA into the mixed interfacial lm. Above the second phase transition (70 C), the intensity of the band at 1724 cm1 decreases strongly, whereas vibrations at 1709 cm1 (Fig. 6b, triangles) and at higher wavenumbers appear (1736 cm1 and above). The second phase transition is therefore assigned to the weakening of the interactions with the carbonyl moieties in the mixed CTA–MA interfacial lm. We therefore assign the second phase transition to the rupture of the hydrogen bond network formed at the surface of the amphiphilic MA–CTAB lm at the interface between water and oil (molten MA). This assignment is further supported by the enthalpy associated with this transition (13 kJ per mole of chain in the MA–CTAB complex), which is consistent with values usually reported for hydrogen bond networks in fatty
This journal is © The Royal Society of Chemistry 2014
Fig. 7 Microscopic observations of a solid sample (T < 52 C, MA– CTAB–10 mM Rhodamine 6G aqueous solution ¼ 70/19/11 weight% mixture). (a) The two types of crystals seen in optical microscopy. (b) Segregation of the mixed MA–CTA lamellar phase (bright regions) from pure myristic acid (dark regions) as observed by confocal microscopy and (c) needle-shape of mixed MA–CTA lamellar phases embedded in myristic acid after 3D-reconstruction from confocal images.
Soft Matter, 2014, 10, 5928–5935 | 5933
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Crystallisation
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Below the low-temperature phase transition (Tonset ¼ 52 C), the microemulsion converts reversibly into the mixture of myristic acid crystals and of the mixed lamellar phase (Fig. 4). The mixed lamellar phase is unable to self-assemble at temperatures above the crystallisation temperature of myristic acid, as shown by SAXS and SANS in the 60–70 C range (Fig. 3 and 4). The formation of the mixed lamellar phase is therefore not driven by the formation of hydrogen bonds, but rather by the crystallisation of myristic acid. Upon crystallisation of the solvent (myristic acid), the segregation of the aqueous nanodomains is forced, as observed upon freezing of colloidal suspensions.27 The mixed MA–CTA lamellar phases form aer coalescence under this effective attractive force. Conversely, upon melting, the mixed lamellar phases disperse again in the liquid MA phase and lose long-range correlation. Consistently with the generic phase diagram proposed to describe the segregation of nanoparticles upon freezing of the solvent,28 the morphology of the aqueous domains in the solid phase is anisotropic (aspect ratio > 5). This is evidenced by optical and uorescence confocal microscopy (Fig. 7) of mixtures containing an aqueous solution of Rhodamine 6G (10 mM) instead of water to label the aqueous phase in confocal images. Comparison between optical and confocal images (Fig. 7a and b) of the same zone shows the two different types of crystals: myristic acid is assigned to the dark areas in confocal images, whereas the bright dye-rich areas are assigned to the mixed MA–CTAB–water crystals. The optical observation conrms the phase segregation between myristic acid and the mixed lamellar phases, as evidenced by the X-ray scattering at small angles (Fig. 4), and 3D reconstruction from the confocal images (Fig. 7c) where an aspect ratio of the mixed MA–CTA–water lamellar crystals is found to be above 5. This situation is consistent with the so-called “unstable” regime of segregation28 expected for the migration of nanometer-sized domains at freezing front velocities typical for myristic acid (20 mm s1 at supercooling of a few degrees29).
Conclusion We therefore have identied the MA–CTA mixtures as potential proton conductors. However, the modest proton conductivity of the as-prepared mixtures (107 S cm1), as compared to the hypothetical upper values (2 S cm1), stresses on the need for proper formulation into a well-organised lm e.g. in terms of percolation. This issue is potentially solved by the bicontinuous microemulsions we have identied in the water–CTAB–MA phase diagram, with molten MA playing both the roles of the oil phase and the co-surfactant. The microemulsions identied in this MA–CTAB–water system show two thermal transitions. The unexpected high-temperature transition between two microemulsions has been assigned to the presence of the mixed MA– CTA lm. As it occurs in a highly imbalanced microemulsion, it has no structural signature. Our rst conclusion is that it suggests a possible and general way to stimulate
5934 | Soft Matter, 2014, 10, 5928–5935
microemulsions (e.g. change in surface properties by temperature) without changing their nanostructure. Furthermore, we have shown that upon cooling, the mixed MA–CTA surfactant lm segregates very quickly from liquid MA to form the mixed lamellar phases. This general understanding opens possible routes to avoid destruction of the nanostructure in solidifying microemulsions, without having necessarily to prevent crystallisation of the continuous phase. Such nanostructure control is a prerequisite in order to use the temperature-driven solidication of microemulsions for the design of bulk materials with properties controlled at the molecular scale, e.g. the connectivity, the composition and the packing of the interfacial lm, and potentially translate directly the 2D conductivity of the lms into high 3D conductivity in bulk materials.
Acknowledgements We acknowledge Marc Detrez for technical support on the PAXE beamline and Patrick Haltebourg for the design of the WAXS setup. This project was funded by the Direction G´ en´ erale de l'Armement and by the CEA-Direction des Sciences de la Mati` ere-Energie program (project E111-9-MISO). The authors thank Prof. P. Barboux (Ecole Nationale Sup´ erieure de Chimie de Paris) for proton conductivity measurements. C. Dejugnat acknowledges the EU for nancial support (FEDER-35477: Nano-objets pour la biotechnologie), and C. Routaboul for her help in IR measurements.
Notes and references 1 K.-D. Kreuer, S. J. Paddison, E. Spohr and M. Schuster, Chem. Rev., 2004, 104, 4637–4678. 2 M. Schuster, T. Rager, A. Noda, K. D. Kreuer and J. Maier, Fuel Cells, 2005, 5, 355–365. 3 M. Prats, J. F. Tocanne and J. Teissie, Eur. J. Biochem., 1987, 162, 379–385. 4 H. Morgan, D. M. Taylor and O. N. Oliveira Jr, Chem. Phys. Lett., 1988, 150, 311–314. 5 H. Morgan, D. Martin Taylor and O. N. Oliveira Jr, Biochim. Biophys. Acta, Biomembr., 1991, 1062, 149–156. 6 G. B´ ealle, J. Jestin and D. Carri` ere, So Matter, 2011, 7, 1084– 1089. 7 B. J¨ onsson, P. Jokela, A. Khan, B. Lindman and A. Sadaghiani, Langmuir, 1991, 7, 889–895. 8 T. Zemb, D. Carriere, K. Glinel, M. Hartman, A. Meister, C. Vautrin, N. Delorme, A. Fery and M. Dubois, Colloids Surf., A, 2007, 303, 37–45. 9 Y. Michina, D. Carri` ere, C. Mariet, M. Moskura, P. Berthault, L. Belloni and T. Zemb, Langmuir, 2009, 25, 698–706. 10 A. Brˆ ulet, D. Lairez, A. Lapp and J.-P. Cotton, J. Appl. Crystallogr., 2007, 40, 165–177. 11 T. Zemb, O. Tach´ e, F. N´ e and O. Spalla, Rev. Sci. Instrum., 2003, 74, 2456–2462. 12 E. Barsoukov and J. R. Macdonald, Impedance Spectroscopy: Theory, Experiment, and Applications, John Wiley & Sons, 2005. 13 V. B. P. Leite, A. Cavalli and O. N. Oliveira, Phys. Rev. E: Stat. Phys., Plasmas, Fluids, Relat. Interdiscip. Top., 1998, 57, 6835–6839.
This journal is © The Royal Society of Chemistry 2014
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Paper
14 E. Maurer, L. Belloni, T. Zemb and D. Carri` ere, Langmuir, 2007, 23, 6554–6560. 15 D. Carriere, L. Belloni, B. Dem´ e, M. Dubois, C. Vautrin, A. Meister and T. Zemb, So Matter, 2009, 5, 4983–4990. 16 P. Khuwijitjaru, S. Adachi and R. Matsuno, Biosci., Biotechnol., Biochem., 2002, 66, 1723–1726. 17 M. Kahlweit, R. Strey, P. Firman, D. Haase, J. Jen and R. Schom¨ acker, Langmuir, 1988, 4, 499–511. 18 M. Teubner and R. Strey, J. Chem. Phys., 1987, 87, 3195–3200. 19 L. Arleth, S. Marcelja and T. Zemb, J. Chem. Phys., 2001, 115, 3923–3936. 20 L. Wolf, H. Hoffmann, T. Teshigawara, T. Okamoto and Y. Talmon, J. Phys. Chem. B, 2012, 116, 2131–2137. 21 M. Duvail, J.-F. Dufrˆ eche, L. Arleth and T. Zemb, Phys. Chem. Chem. Phys., 2013, 15, 7133–7141. 22 R. Strey, Colloid Polym. Sci., 1994, 272, 1005–1019.
This journal is © The Royal Society of Chemistry 2014
Soft Matter
23 X. Wen and E. I. Franses, J. Colloid Interface Sci., 2000, 231, 42–51. 24 S. T. Shipman, P. C. Douglass, H. S. Yoo, C. E. Hinkle, E. L. Mierzejewski and B. H. Pate, Phys. Chem. Chem. Phys., 2007, 9, 4572–4586. 25 S. Lifson, A. T. Hagler and P. Dauber, J. Am. Chem. Soc., 1979, 101, 5111–5121. 26 M. A. Hartmann, R. Weinkamer, T. Zemb, F. D. Fischer and P. Fratzl, Phys. Rev. Lett., 2006, 97, 018106. 27 S. Deville, E. Saiz, R. K. Nalla and A. P. Tomsia, Science, 2006, 311, 515–518. 28 S. Deville, E. Maire, G. Bernard-Granger, A. Lasalle, A. Bogner, C. Gauthier, J. Leloup and C. Guizard, Nat. Mater., 2009, 8, 966–972. 29 K. Fukui and K. Maeda, J. Chem. Phys., 2000, 112, 1554– 1559.
Soft Matter, 2014, 10, 5928–5935 | 5935
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Cite this: Soft Matter, 2014, 10, 5928
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Quenched microemulsions: a new route to proton conductors Cecile Noirjean,a Fabienne Testard,a Jacques Jestin,b Olivier Tache´,a Christophe Dejugnatc and David Carriere*a Solid-state proton conductors operating under mild temperature conditions (T < 150 C) would promote the use of electrochemical devices as fuel cells. Alternatives to the water-sensitive membranes made of perfluorinated sulfonated polymers require the use of protogenic moieties bearing phosphates/ phosphonates or imidazole groups. Here, we formulate microemulsions using water, a cationic surfactant (cetyltrimethyl ammonium bromide, CTAB) and a fatty acid (myristic acid, MA). The fatty acid acts both as an oil phase above its melting point (52 C) and as a protogenic moiety. We demonstrate that the mixed MA–CTA film presents significant proton conductivity. Furthermore, bicontinuous microemulsions are found in the water–CTAB–MA phase diagram above 52 C, where molten MA plays both the role of the oil phase and the co-surfactant. This indicates that the hydrogen-bond rich MA–
Received 18th April 2014 Accepted 4th June 2014
CTA film can be formulated in the molten phase. The microemulsion converts into a lamellar phase upon solidification at room temperature. Our results demonstrate the potential of such self-assembled
DOI: 10.1039/c4sm00849a
materials for the design of bulk proton conductors, but also highlight the necessity to control the
www.rsc.org/softmatter
evolution of the nanostructure upon solidification of the oil phase.
Introduction Fuel cells, which convert chemical energy from fuel (e.g., hydrogen or methanol) into electric energy, exhibit performances directly linked to the specic properties of the separator between the anode and the cathode. In PEMFCs (Proton Exchange Membrane Fuel Cells), the separating membrane must show bulk proton conductivity as high as possible, in addition to a lack of electronic conductivity and low permeability to gases and/or liquids.1 The most famous benchmark membrane operating at low temperatures (10 nm). This demonstrates that phase separation between the lamellar phases occurs, similar to the emulsication failure in the classical all-liquid microemulsions stabilized e.g. by n-alkyl poly(ethoxy) surfactants.17,22 In an opposite manner, the second phase transition is assigned to the melting of the mixed amphiphilic lm, but occurs without detectable structural changes (i.e. no curvature change): neither the microemulsion periodicity nor its correlation length as determined are affected (Fig. 3a and b, and Table 1) despite the well-dened endothermic peak (Fig. 5). This lack of response originates from the nature of the high-temperature transition occurring in the lm at 70 C, which we have elucidated using IR spectroscopy as a function of temperature.
Elucidation of the higher temperature transition At low temperature (T < 52 C), the mixtures therefore consist of a solid mixture of myristic acid and the MA–CTA–H2O lamellar phase. These lamellar structures vanish simultaneously and form the microemulsion at a melting temperature that coincides with that of myristic acid (Tm ¼ 52 C). This suggests that myristic acid alone melts at the rst transition and that the mixed lamellar phase organizes at the water/liquid MA interface. The second thermodynamic transition (Tm ¼ 70 C) is not accompanied by any detectable change in the nanostructure. This suggests that it corresponds to a transition of the MA–CTA interfacial lm. This interpretation is supported by infrared spectroscopy results as a function of temperature (Fig. 6). In the 1600–1800 cm1 range, characteristic of the carbonyl C]O vibrations (stretching), three series of spectra are observed. They are respectively characteristic of the mixtures below and above both thermal transitions. Below 52 C, the spectra are dominated by the vibrations at 1689 cm1 and 1701 cm1, assigned to MA cyclic dimers in the solid phase,23 and a band at 1724 cm1. The latter wavenumber value is an intermediate between that of the strongly bound cyclic MA dimers, and that of the free monomers24 (1774 cm1 and 1785 cm1). The band at 1724 cm1 is therefore assigned to the C]O vibrations in the mixed CTA–MA lamellar phase. Above the low-temperature phase transition (52 C), the vibrations assigned to the myristic acid cyclic dimers (1689 cm1 and 1701 cm1) strongly decrease (Fig. 6b, squares), whereas the vibration assigned to the MA–CTA complex
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acids.25 Furthermore, the formation or destruction of such a hydrogen bond network is expected to alter only marginally the bending modulus of a mixed equimolar MA–CTA bilayer.26 Assuming similar behaviour for monolayers, we elucidate the absence of nanostructure modication as the higher-temperature transition is crossed (Fig. 3 and 4).
Fig. 6 Infrared spectra of a MA–CTAB–H2O ¼ 70/19/11 weight% mixture as a function of temperature. (a) IR spectra in the carbonyl C]O stretching vibration region at different temperatures (full lines: in the 25–55 C range; dashed lines: in the 55–65 C range; dotted lines: in the 70–80 C range). (b) Relative area of the peaks as a function of temperature (squares: myristic acid dimers, 1701 and 1689 cm1; circles: 1724 cm1; triangles: 1709 cm1).
increases (1724 cm1, Fig. 6b, circles). This is consistent with the melting of the solid MA, and with an increased fraction of MA in interaction with CTAB by uptake of MA into the mixed interfacial lm. Above the second phase transition (70 C), the intensity of the band at 1724 cm1 decreases strongly, whereas vibrations at 1709 cm1 (Fig. 6b, triangles) and at higher wavenumbers appear (1736 cm1 and above). The second phase transition is therefore assigned to the weakening of the interactions with the carbonyl moieties in the mixed CTA–MA interfacial lm. We therefore assign the second phase transition to the rupture of the hydrogen bond network formed at the surface of the amphiphilic MA–CTAB lm at the interface between water and oil (molten MA). This assignment is further supported by the enthalpy associated with this transition (13 kJ per mole of chain in the MA–CTAB complex), which is consistent with values usually reported for hydrogen bond networks in fatty
This journal is © The Royal Society of Chemistry 2014
Fig. 7 Microscopic observations of a solid sample (T < 52 C, MA– CTAB–10 mM Rhodamine 6G aqueous solution ¼ 70/19/11 weight% mixture). (a) The two types of crystals seen in optical microscopy. (b) Segregation of the mixed MA–CTA lamellar phase (bright regions) from pure myristic acid (dark regions) as observed by confocal microscopy and (c) needle-shape of mixed MA–CTA lamellar phases embedded in myristic acid after 3D-reconstruction from confocal images.
Soft Matter, 2014, 10, 5928–5935 | 5933
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Crystallisation
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Below the low-temperature phase transition (Tonset ¼ 52 C), the microemulsion converts reversibly into the mixture of myristic acid crystals and of the mixed lamellar phase (Fig. 4). The mixed lamellar phase is unable to self-assemble at temperatures above the crystallisation temperature of myristic acid, as shown by SAXS and SANS in the 60–70 C range (Fig. 3 and 4). The formation of the mixed lamellar phase is therefore not driven by the formation of hydrogen bonds, but rather by the crystallisation of myristic acid. Upon crystallisation of the solvent (myristic acid), the segregation of the aqueous nanodomains is forced, as observed upon freezing of colloidal suspensions.27 The mixed MA–CTA lamellar phases form aer coalescence under this effective attractive force. Conversely, upon melting, the mixed lamellar phases disperse again in the liquid MA phase and lose long-range correlation. Consistently with the generic phase diagram proposed to describe the segregation of nanoparticles upon freezing of the solvent,28 the morphology of the aqueous domains in the solid phase is anisotropic (aspect ratio > 5). This is evidenced by optical and uorescence confocal microscopy (Fig. 7) of mixtures containing an aqueous solution of Rhodamine 6G (10 mM) instead of water to label the aqueous phase in confocal images. Comparison between optical and confocal images (Fig. 7a and b) of the same zone shows the two different types of crystals: myristic acid is assigned to the dark areas in confocal images, whereas the bright dye-rich areas are assigned to the mixed MA–CTAB–water crystals. The optical observation conrms the phase segregation between myristic acid and the mixed lamellar phases, as evidenced by the X-ray scattering at small angles (Fig. 4), and 3D reconstruction from the confocal images (Fig. 7c) where an aspect ratio of the mixed MA–CTA–water lamellar crystals is found to be above 5. This situation is consistent with the so-called “unstable” regime of segregation28 expected for the migration of nanometer-sized domains at freezing front velocities typical for myristic acid (20 mm s1 at supercooling of a few degrees29).
Conclusion We therefore have identied the MA–CTA mixtures as potential proton conductors. However, the modest proton conductivity of the as-prepared mixtures (107 S cm1), as compared to the hypothetical upper values (2 S cm1), stresses on the need for proper formulation into a well-organised lm e.g. in terms of percolation. This issue is potentially solved by the bicontinuous microemulsions we have identied in the water–CTAB–MA phase diagram, with molten MA playing both the roles of the oil phase and the co-surfactant. The microemulsions identied in this MA–CTAB–water system show two thermal transitions. The unexpected high-temperature transition between two microemulsions has been assigned to the presence of the mixed MA– CTA lm. As it occurs in a highly imbalanced microemulsion, it has no structural signature. Our rst conclusion is that it suggests a possible and general way to stimulate
5934 | Soft Matter, 2014, 10, 5928–5935
microemulsions (e.g. change in surface properties by temperature) without changing their nanostructure. Furthermore, we have shown that upon cooling, the mixed MA–CTA surfactant lm segregates very quickly from liquid MA to form the mixed lamellar phases. This general understanding opens possible routes to avoid destruction of the nanostructure in solidifying microemulsions, without having necessarily to prevent crystallisation of the continuous phase. Such nanostructure control is a prerequisite in order to use the temperature-driven solidication of microemulsions for the design of bulk materials with properties controlled at the molecular scale, e.g. the connectivity, the composition and the packing of the interfacial lm, and potentially translate directly the 2D conductivity of the lms into high 3D conductivity in bulk materials.
Acknowledgements We acknowledge Marc Detrez for technical support on the PAXE beamline and Patrick Haltebourg for the design of the WAXS setup. This project was funded by the Direction G´ en´ erale de l'Armement and by the CEA-Direction des Sciences de la Mati` ere-Energie program (project E111-9-MISO). The authors thank Prof. P. Barboux (Ecole Nationale Sup´ erieure de Chimie de Paris) for proton conductivity measurements. C. Dejugnat acknowledges the EU for nancial support (FEDER-35477: Nano-objets pour la biotechnologie), and C. Routaboul for her help in IR measurements.
Notes and references 1 K.-D. Kreuer, S. J. Paddison, E. Spohr and M. Schuster, Chem. Rev., 2004, 104, 4637–4678. 2 M. Schuster, T. Rager, A. Noda, K. D. Kreuer and J. Maier, Fuel Cells, 2005, 5, 355–365. 3 M. Prats, J. F. Tocanne and J. Teissie, Eur. J. Biochem., 1987, 162, 379–385. 4 H. Morgan, D. M. Taylor and O. N. Oliveira Jr, Chem. Phys. Lett., 1988, 150, 311–314. 5 H. Morgan, D. Martin Taylor and O. N. Oliveira Jr, Biochim. Biophys. Acta, Biomembr., 1991, 1062, 149–156. 6 G. B´ ealle, J. Jestin and D. Carri` ere, So Matter, 2011, 7, 1084– 1089. 7 B. J¨ onsson, P. Jokela, A. Khan, B. Lindman and A. Sadaghiani, Langmuir, 1991, 7, 889–895. 8 T. Zemb, D. Carriere, K. Glinel, M. Hartman, A. Meister, C. Vautrin, N. Delorme, A. Fery and M. Dubois, Colloids Surf., A, 2007, 303, 37–45. 9 Y. Michina, D. Carri` ere, C. Mariet, M. Moskura, P. Berthault, L. Belloni and T. Zemb, Langmuir, 2009, 25, 698–706. 10 A. Brˆ ulet, D. Lairez, A. Lapp and J.-P. Cotton, J. Appl. Crystallogr., 2007, 40, 165–177. 11 T. Zemb, O. Tach´ e, F. N´ e and O. Spalla, Rev. Sci. Instrum., 2003, 74, 2456–2462. 12 E. Barsoukov and J. R. Macdonald, Impedance Spectroscopy: Theory, Experiment, and Applications, John Wiley & Sons, 2005. 13 V. B. P. Leite, A. Cavalli and O. N. Oliveira, Phys. Rev. E: Stat. Phys., Plasmas, Fluids, Relat. Interdiscip. Top., 1998, 57, 6835–6839.
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 04 June 2014. Downloaded by Washington State University Libraries on 26/10/2014 03:25:59.
Paper
14 E. Maurer, L. Belloni, T. Zemb and D. Carri` ere, Langmuir, 2007, 23, 6554–6560. 15 D. Carriere, L. Belloni, B. Dem´ e, M. Dubois, C. Vautrin, A. Meister and T. Zemb, So Matter, 2009, 5, 4983–4990. 16 P. Khuwijitjaru, S. Adachi and R. Matsuno, Biosci., Biotechnol., Biochem., 2002, 66, 1723–1726. 17 M. Kahlweit, R. Strey, P. Firman, D. Haase, J. Jen and R. Schom¨ acker, Langmuir, 1988, 4, 499–511. 18 M. Teubner and R. Strey, J. Chem. Phys., 1987, 87, 3195–3200. 19 L. Arleth, S. Marcelja and T. Zemb, J. Chem. Phys., 2001, 115, 3923–3936. 20 L. Wolf, H. Hoffmann, T. Teshigawara, T. Okamoto and Y. Talmon, J. Phys. Chem. B, 2012, 116, 2131–2137. 21 M. Duvail, J.-F. Dufrˆ eche, L. Arleth and T. Zemb, Phys. Chem. Chem. Phys., 2013, 15, 7133–7141. 22 R. Strey, Colloid Polym. Sci., 1994, 272, 1005–1019.
This journal is © The Royal Society of Chemistry 2014
Soft Matter
23 X. Wen and E. I. Franses, J. Colloid Interface Sci., 2000, 231, 42–51. 24 S. T. Shipman, P. C. Douglass, H. S. Yoo, C. E. Hinkle, E. L. Mierzejewski and B. H. Pate, Phys. Chem. Chem. Phys., 2007, 9, 4572–4586. 25 S. Lifson, A. T. Hagler and P. Dauber, J. Am. Chem. Soc., 1979, 101, 5111–5121. 26 M. A. Hartmann, R. Weinkamer, T. Zemb, F. D. Fischer and P. Fratzl, Phys. Rev. Lett., 2006, 97, 018106. 27 S. Deville, E. Saiz, R. K. Nalla and A. P. Tomsia, Science, 2006, 311, 515–518. 28 S. Deville, E. Maire, G. Bernard-Granger, A. Lasalle, A. Bogner, C. Gauthier, J. Leloup and C. Guizard, Nat. Mater., 2009, 8, 966–972. 29 K. Fukui and K. Maeda, J. Chem. Phys., 2000, 112, 1554– 1559.
Soft Matter, 2014, 10, 5928–5935 | 5935
